1. Field of the Invention
The present invention relates to a disk pack module of a magnetic disk memory in which data disks, separated from one another by spacer rings, are slipped onto a hub which is rotatably arranged in a housing, the disks being located against a hub flange which projects in the radial direction and being clamped thereto in a non-positive manner by way of tension plate.
2. Description of the Prior Art
The technical development of magnetic disk memories, whether hard disk memories or moving head disk memories, as peripheral storage modules in modern data processing systems is continuously accompanied by the foremost desire to increase the storage capacity of such bulk memories. Efforts are therefore exerted, first of all, in order to achieve an optimally high track and bit density per disk surface; on the other hand, nothing is spared in order to accommodate an optimally-great plurality of data disks, given a prescribed mounting space of the magnetic disk memory. Both alternatives of enlarging the storage capacity of such peripheral modules, however, make certain, necessary requirements of the structural format of a magnetic disk memory.
The European patent applications 0 151 260, 0 151 259, 0 151 258 and 0 151 256, disclose pertinent solutions for the structural format of magnetic disk memories in which an internal motor concept is realized. A drive motor is thereby indicated in a receptacle device for the data disks that form a disk stack module together with the motor. A plurality of data disks can be accommodated in a housing with dense packing in this manner. All data disks are simultaneously placed in rotation with the common drive.
The fact that such a drive, integrated into the receptacle device, and referred to as an internal motor, generates stray magnetic fields and not without problems for the storage of the data on the disk. It is consequently critical for a faultless operation in this case that the data disks be magnetically decoupled from the receptacle device constructed as a hub. To this end, the data disks are manufactured of aluminum and the hub is manufactured of soft iron.
One disadvantage of this known solution, however, is a certain temperature sensitivity. Due to temperature fluctuations occurring during transport, but also occurring during operation of a magnetic disk memory, material stresses occur due to the coefficients of thermal expansion of aluminum and iron that differ by about the factor two. It cannot be guaranteed that these material stresses will not assume an order of magnitude that ultimately results in a slipping of the data disks.
The Coulomb coefficient of friction is lent considerable significance in this slipping. Since the coefficients of friction expand greatly, slipping only occurs coaxially relative to the rotational axis of the data disks in exceptional cases. Based on manufacture, the data disks often exhibit a certain eccentricity that can still be tolerated. A further eccentricity produced by the scatter of the Coulomb efficients of friction is added thereto as a consequence of the temperature-dependent material stresses. This eccentricity of the data disks that is again highly likely to vary over the course of the operating time lies on an order of magnitude that can lead to errors when reading the data stored on the disk given magnetic disk memories having high track density.
When the eccentricity of the data disks reaches an order of magnitude of 10 .mu.m as a consequence of temperature fluctuations under the described operating conditions, given track densities that are currently standard, even a servo control for the tracking of the read heads that is standard in current high-capacity disk memories can no longer track with adequate precision.
The drive motor in another group of traditional magnetic disk memories is constructed as an external motor, i.e. the data disks are driven by a motor that is externally flanged to the housing of the magnetic disk memory. In this structure of a magnetic disk memory, both the hub and the data disks can be manufactured of aluminum. The advantages, first of all, of not having to additionally shield the stray magnetic fields of the motor and, secondly, of not having to consider the occurrence of any temperature-dependent material stresses are opposed by the disadvantage of a lower storage capacity given a prescribed mounting space for the disk memory.
U.S. Pat. No. 4,519,010, fully incorporated herein by this reference, further discloses a magnetic disk memory comprising an internal motor in which the hub and the data disks are likewise manufactured of identical material. As a result of the identical coefficients of thermal expansion, no thermal material stresses thereby arise in such a structure at the seeping surfaces of the data disks on the hub. However, a magnetic shield for the stray magnetic fields deriving from the internal motor is required in this case so that the data disks are magnetically decoupled. One part of the shield is composed of a magnetic reflux or return ring of magnetically-conductive material, preferably soft iron, that surrounds the permanent magnet of the drive motor. The entire internal motor is ultimately magnetically shielded from the data disks by further protective rings. An unreasonably-high structural expense and high space requirement in order to assure the magnetic shielding of the data disks are disadvantageous in this solution.
Alternatively thereto, the German application 35 15 059, fully incorporated herein by this reference, and corresponding to the British patent specification 21 58 633, discloses a possibility of compensating the mechanical and thermal stressing during transport and during operation of the disk memory that occurs in the internal motor design. The relative disk location of the data disk manufactured of aluminum relative to an iron hub should thereby be avoided by the integration of a clamp device that is flexibly designed in order to achieve constant friction conditions. A cup-shaped clamp, constructed slightly resilient, is provided and is connected to the iron hub with a threaded bolt and mechanically clamps the data disk. What is thereby suppose to be achieved is that the Coulomb friction in the critical seating region between the hub and the data disk is greater than between the data disk and the clamp. The clamp device should therefore yield given the occurrence of mechanical and thermal stresses without a radial dislocation occurring for the data disk. Opposing this described solution, however, is that the required constancy in the friction condition is not assured without further measures given frequent temperature changes. Added thereto is that the structural requirements made of a magnetic disk memory of the type set forth are only unsatisfactorily resolved by such a clamp device.